Air purge valves are designed to be installed in liquid flow systems such as, for example, water main distribution lines or sewage collection systems, or liquid tanks, and are intended to discharge air (typically in water supply systems) or other gasses (e.g. in sewage systems or thick liquid supply systems), thus avoiding the formation and accumulation of gas pockets and bubbles which interfere with the liquid flow and which can also damage accessories and components of the liquid system. On the other hand, when the liquid system is drained, it is required to air the lines so as to avoid their collapse under rapid vacuum build-up.
A basic requirement for gas purge valves is their ability to effectively and rapidly discharge both large and small quantities of gas whilst, at the same time, being or becoming sealed against liquid discharge. Conventional air purge valves are formed with a gas discharge outlet through which the gases are discharged, but which become sealed against liquid discharge by a float located in a valve housing and which becomes pressed against the outlet so as to seal it with a rising level of liquid in the valve housing.
Such valves, when provided with a relatively small discharge outlet are effective for the discharge of small quantities of gas, but cannot cope when large quantities have to be discharged. Where, however, in order to render the valve capable of handling large quantities of gas it is provided with a large discharge outlet (and, consequently, a large dimensioned float), problems arise in ensuring that the valve can readily and rapidly discharge relatively small quantities of gas after the discharge outlet has been sealed against liquid outflow. Thus, once the valve housing is filled with liquid and the float has been pressed against the relatively large outlet so as to seal it, the valve will only reopen once the pressure in the housing has dropped to atmospheric pressure and, as a consequence, such a valve cannot be used for the continuous venting of relatively small amounts of air.
Moreover, such valves have the drawback of being substantially sensitive to the presence of dirt, grit, etc., particularly where manufacturing tolerances or erosion of various components, built-up of dirt or scale, etc., greatly influence the behavior of the float and its response to changes of the fluid flowing therethrough (liquid or gas). Thus, the performance of such air purge valves is somewhat deficient and they may malfunction.
A large variety of gas valves have been proposed for gas purge valves capable of effectively and rapidly discharging both relatively small and large quantities of gas. Such a proposal is to be found in U.S. Pat. Nos. 4,770,201 and 6,105,608. Prior art arrangements, whilst allowing for the effective and speedy opening of the outlet aperture for rapid discharge of relatively small quantities of gas as well as its complete opening for the discharge of large quantities, are nevertheless vulnerable in particular when installed in lines through which dirt flows along with the liquid, e.g. sewage lines.
However, in valves of the type comprising a float member received within the valve housing and being articulated with an outlet sealing means, there is provided some guidance to facilitate regular and smooth displacement of the sealing means. For that purpose it has been suggested to provide a support rod coaxially extending with the sealing means and axially displaceable within an external support bushing. This arrangement however is prone to malfunctioning upon deformation of the support rod and upon entering of dirt to the vicinity of the bushing. Even more so, the axial guidance does not assist in displacement of the sealing means, but rather may cause an obstacle to normal operation thereof.